Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $48.58   12.667%   $54.7336   $54.73   $54.75   $54.70  
  Purchase #2 $41.89   11.490%   $46.7032   $46.70   $46.70   $46.70  
  Purchase #3 $6.48   4.267%   $6.7565   $6.76   $6.75   $6.80  
  Purchase #4 $58.94   4.666%   $61.6901   $61.69   $61.70   $61.70  
  Purchase #5 $35.81   8.870%   $38.9863   $38.99   $39.00   $39.00  
  Purchase #6 $225.60   6.840%   $241.031   $241.03   $241.05   $241.00  
  Purchase #7 $209.27   6.584%   $223.0483   $223.05   $223.05   $223.00  
  7 purchase totals = $626.57       $672.9490   $672.95   $673.00   $672.90